Many types of input devices are presently available for performing operations in a computing system, such as buttons or keys, mice, trackballs, joysticks, touch sensor panels, touch screens and the like. Touch screens, in particular, are becoming increasingly popular because of their ease and versatility of operation as well as their declining price. Touch screens can include a touch sensor panel, which can be a clear panel with a touch-sensitive surface, and a display device such as a liquid crystal display (LCD) that can be positioned partially or fully behind the touch sensor panel so that the touch-sensitive surface can cover at least a portion of the viewable area of the display device. Touch screens can allow a user to perform various functions by touching the touch sensor panel using a finger, stylus or other object at a location often dictated by a user interface (UI) being displayed by the display device. In general, touch screens can recognize a touch and the position of the touch on the touch sensor panel, and the computing system can then interpret the touch in accordance with the display appearing at the time of the touch. Thereafter, the computing system can perform one or more actions based on the touch. In the case of some touch sensing systems, a physical touch on the display may not be needed to detect a touch. For example, in some capacitive-type touch sensing systems, fringing electrical fields used to detect touch can extend beyond the surface of the display, and objects approaching near the surface may be detected near the surface without actually touching the surface.
Touch sensor panels can include an array of touch sensors capable of detecting touches (the touching by an object such as a finger upon a touch-sensitive surface). Some touch sensor panels are able to detect multiple touches (e.g., the touching of multiple fingers upon a touch-sensitive surface at distinct locations at or about the same time) and near touches (e.g., fingers within the near-field detection capabilities of their touch sensors), and identify and track their locations.
In reality, however, not all touches detected on a touch sensor panel are intended user input. For example, water on the surface of the touch sensor panel can be detected as a touch. In particular, water on a touch-sensitive surface in contact with a metal housing of the device or a finger can be grounded and appear as a touch by a finger. As a result, water (or other unintentional touches) can result in unintended behavior by the device. This can negatively affect user experience, particularly in wet environments.